1. Technical Field
The present invention relates to a rotary machine such as a motor or generator, in particular an improvement of the bearing of a rotary machine of inner rotor type.
2. Description of the Prior Art
Some bearing apparatus of the prior art employed in the rotary machine such as a motor or generator has such a structure as illustrated in FIG. 2. In this structure, a pair of ball bearings are provided on the shaft 31. These bearings comprise an inner race, an outer race, and balls disposed therebetween. The inner race of each bearing is secured to the shaft 31.
The supreme desire of the rotary machine such as the motor or generator is miniaturising thereof. Further, it is desired to miniaturise the bearing apparatus employed in these rotary machine.
One of the measures for miniaturising the bearing apparatus is to minuaturise the ball bearings to reduce the outer diameter of the outer race. However, reducing of the size of ball bearings leads to a reduction of the inner diameter of the ball bearings, so that also reduced is the diameter of the shaft on which the bearings are provided. This may raise the problems of the decreasing of the rigidity of the shaft, the decreasing of the durability of the rotary machine, and spoiling of the anti-vibration property.
On the other hand, there is a motor as rotary machine in which the inner race of the one of the bearings is eliminated by forming a recess 42a for rolling contact with the balls on the outer periphery of the shaft 41 as shown in FIG. 3.
The embodiment of the prior art as shown in FIG. 3, balls for the one side row are interposed between the inner rolling contact recess 42a formed directly on the outer peripheral surface of the shaft 41 at the upper oprtion thereof and the outer rolling contact recess 42a formed on the interior surface of the sleeve shaped outer race 43. Fitted on the reduced diameter shaft portion of the shaft 41 is a ball bearing 44 in which balls for the other side row are disposed between inner and outer races.
The lower end portion of the sleeve shaped outer race 43 and the outer race of the ball bearing 44 are fixedly fitted into the hole provided through the base plate 45 so that the bearing apparatus is standing vertically to the base. An stator 46 is mounted around the outer periphery of the sleeve shaped outer race 43, and an rotor 47 having magnets 47a secured on the interior surface thereof is fixedly fitted over the top end of the shaft 41.
In the structure of the motor as shown in FIG. 3, can be achieved the advantage that the diameter of the sleeve shaped outer race 43 can be reduced without reducing the diameter of the shaft 41, since the inner race for the one side row is not required.
However, in the bearing apparatus for the motor as illustrated in FIG. 3, the rotor can not be attached to the shaft, since the shaft 41 is enclosed for almost the entire length thereof within the sleeve shaped outer race 43, so that the structure of FIG. 3 can be applied only to the motor of outer rotor type.
The outer diameter of the motor of outer rotor type is larger than that of the motor of inner rotor type by the difference between the outer diameter of the sleeve shaped outer race and the outer diameter of the shaft, and thus the miniaturising of the motor can not be achieved.
Although the sleeve shaped outer race of the motor of FIG. 3 is required to machine in high precision, it is difficult to machine the outer race to have high precision roundness since the spacing between the outer rolling contact recess 42a and the end of the outer race fixed to the base 45 i.e. the length of the sleeve shaped outer race is a relatively large. Cosequently, the structure of FIG. 3 is not suitable for mass production.
Accordingly the object of the present invention is to provide a rotary machine of inner rotor type having a sufficient shaft rigidity, a high durability; and anti-vibration property.